To understand how angina is classified, you should know first that angina is not a disease, but rather a manifestation of a heart condition. Thus, the classification into types is based on how symptoms are manifested and how the pathology occurs.
The main types of angina are:
- Stable angina
- Unstable angina
- Prinzmetal’s variant angina
- Microvascular angina
There are some other minor types, but they are incredibly rare compared to the above. Now, let’s take each one of them and discuss it in detail.
Types of angina
It is the most common type of angina and the most important cause of chest pain. It results from the narrowing of the coronary arteries -the main blood supply to the heart muscle- from chronic deposition of fat in their walls, causing plaques and decreasing the diameter of the vessels in a process known as atherosclerosis. The pathology of coronary artery narrowing is gradual and takes years to develop. The condition remains asymptomatic until the narrowing reaches the threshold at which it starts causing the characteristic anginal pain. This pain is a consequence of not meeting the oxygen supply requirements of the blood and may lead to ischemia. The patient can predict his or her attacks as they have specific “triggers” that include:
- Physical exercise
- Emotional stress
- Cold exposure
- Heavy meals, especially consisting of fatty foods.
Attacks are usually brief (not more than 10 minutes) and are relieved by medications as nitrates and by rest. Since stable angina is a gradual process, symptoms tend to worsen over time, and the effort needed to cause symptoms become less until it reaches the level of occurring at rest.
2. Unstable angina
Unstable angina is the inevitable consequence of the stable type when the risk factors and the pathology are not controlled. It occurs due to progressive atherosclerosis and narrowing of the coronaries that aggravates the symptoms until they occur at rest, lasting longer than 10 minutes, becoming more severe, and not being relieved by rest or nitrates. The reason for this sudden narrowing is the blockage of an already narrowed artery or arteries by a blood clot.
Under normal circumstances, clots don’t form because the blood vessel’s wall is “smooth,” composed of perfectly lined cells of the vessel wall. However, in the case of unstable angina, the fatty plaques already present in the coronary arteries walls are “disrupted” or ruptured, giving blood platelets the needed “rough” surface to aggregate and form a clot.
Unstable angina is a medical emergency and a warning sign that a heart attack -medically known as myocardial infarction- is likely to follow. Thus, unstable angina is grouped into what is called “acute coronary syndrome” along with myocardial infarction. The only difference between them is the evidence of heart cells’ death, which is only present in myocardial infarction.
3. Prinzmetal’s variant angina
It is a rare condition and, contrary to the stable and unstable types of angina, Prinzmetal’s angina is not caused by atherosclerosis as a primary pathology. Instead, it is triggered by the “spasm” of coronary arteries that will suddenly cause a drop of blood supply to the heart. Attacks are acute and unpredictable. Triggers of this spasm include:
- Cold exposure
- Emotional stress
- Cocaine use
- Other medications
They may also be triggered without a specific cause. Prinzmetal’s angina can occur in healthy or diseased coronary arteries by atherosclerosis, and is commonly associated with other conditions related to the spasm of other arteries in the body, as in the case of migraine headaches -where spasm of arteries in the brain is the leading cause- and Reynaud’s phenomenon (excessive spasm of your fingers’ arteries leading to a bluish discoloration and pain, more common in response to cold temperatures). Since both migraines and Reynaud’s are more common among females, Prinzmetal’s angina has a higher prevalence among females. The condition has a better outcome than unstable angina and is manageable by medications.
4. Microvascular angina
Microvascular angina is a type of angina where the narrowing occurs in the small branches of the main coronary arteries -hence the prefix “micro”- rather than the primary arteries like the previous types. It is characterized by chest pain that usually lasts for longer compared to stable angina, and takes a longer time to be relieved after rest or nitrates intake. Microvascular angina is diagnosed by exclusion of the other types through investigations and follow-up.